Abstract: The model of inertia friction welding of FGH96/GH4169 was established and the forming process of the deformed grains in the joint was analyzed. The results show that the friction heat leads to the formation of the plastic laver near the interface, the plastic laver flow under the stress and results in the formation of the deformed grains. Eventually the boundary of the deformed grains are broken, and the weld zone consists of reined and equiaxed grains. The plastic metals on the interface flow on radial direction and ae squeezed to form the flash on the edge. The flash can take the inclusions out friction interface shows self clean effect.